Patients and methods Twelve patients (aged 36-63 years) with male erectile dysfunction of no established organic cause were entered into a double-blind, randomized, placebo-controlled, crossover study which was conducted in two phases. In the first phase (four-way crossover), treatment efficacy was evaluated by measurements of penile rigidity using penile plethysmography during visual sexual stimulation at different doses of sildenafil (10, 25 and 50 mg or placebo). In the second phase (two-way crossover), efficacy was assessed by a diary record of penile erectile activity after single daily doses of sildenafil (25 mg) or placebo for 7 days.

Results The mean (95% confidence interval, CI) duration of rigidity of >80% at the base of the penis was 1.3 min (0.4-3.1) in patients on placebo, 3.5 min (1.6-7.3; P=0.009) on 10 mg, 8.0 min (3.7-16.7; P=0.003) on 25 mg and 11.2 min (5.6-22.3; P <0.001) on 50 mg of sildenafil. The mean (95% CI) duration of rigidity of >80% at the tip of the penis was 1.2 min (0.4-2.7) on placebo and 7.4 min (2.4-8.5; P=0.001) on 50 mg sildenafil. from the diary record of daily erectile activity, the mean (95% CI) total number of erections was significantly higher in patients receiving sildenafil was 6.1 (3.2-11.4), compared with 1.3 (0.5-2.7) in those on placebo; 10 of 12 patients reported improved erectile activity while receiving sildenafil, compared with two of 12 on placebo (P=0.018). Six patients on active treatment and five on placebo reported mild and transient adverse events which included headache, dyspepsia and pelvic musculo-skeletal pain.

Conclusion These results show that sildenafil is a well tolerated and effective oral therapy for male erectile dysfunction with no established organic cause and may represent a new class of peripherally acting drug for the treatment of this condition.